1. Field of the Invention
The present invention relates to a method for determining electrode spacing and operating conditions for in situ electrokinetic soil remediation and/or soil treatment.
2. Background of the Related Art
Electrokinetic remediation of contaminated soil is an emerging in situ technology for soil cleanup, which is based on the electrically induced transport of contaminants in soil. An electric field applied between electrodes positioned in the soil induces electrokinetic phenomena in soil including electromigration, electroosmosis and electrophoresis. The electrical transport induced in soil is utilized for controlling the horizontal and/or vertical removal of contaminants from soils of variable hydraulic permeability and moisture content, or the introduction and distribution of reagents into the soil which allow in situ contaminant degradation enhancement of the contaminant solubility, immobilization of contaminants or attainment of an optimum pH in soil during the treatment process. Electrokinetic remediation processes have a number of attractive features including the ability to control the movement of charged, anionic and cationic, as well as non-charged species. Furthermore electrokinetic remediation is able to operate successfully in different soil types, including low hydraulic permeability, clay containing soils. Electrokinetic remediation finds many applications for treatment of soil, such as soils polluted by heavy metals, radionuclides, organic contaminants, or a combination of several pollutants.
Application of an in situ technology for soil cleanup requires knowledge of hydrogeological and the chemical and physical parameters of both the soil and the contaminants at the treatment site. To simplify the design of the electrokinetic remediation process and determine a working amount of chemicals and their concentrations needed for an in situ cleanup process a short bench-scale treatability study is usually performed using contaminated soil from the site. Such treatability studies are well known in bioremediation and in situ soil flushing technologies.
In electrokinetics, data from these types of studies allows the determination of the type and quantity of additives needed to be added to the soil to enhance the electrokinetic remediation process as well as to determine whether the direction of contaminant movement is toward the anode or cathode. However, several operational parameters are strictly dependent on soil conductivity, which is difficult to simulate in a bench-scale experiment due to different packing, porosity of the soil and chemical properties of the pore fluid/soil interface encountered in the field. Thus, not all the design parameters can be accurately determined at the bench scale and used in the scale-up for the electrokinetic remediation process design in the field.
Establishing electroosmotic flow is important in some processes, such as removing organic contaminants and enhancing metal or radionuclide removal from soil. Because the electroosmotic flow depends on the surface properties of soil and the voltage applied between the electrodes, results obtained using only mathematical models or laboratory studies are inconsistent with results obtained in the field. Both the surface properties of soil and the voltage applied between the electrodes are dependent on the voltage or current which can be applied through the soil having particular resistance.
Because the spacing and configuration of the electrode wells directly affects the cost of cleaning the soil as well as the efficiency and uniformity of the soil cleanup, it would be very useful to have a method for determining an efficient or required spacing and configuration of the electrode wells for successful electrokinetic soil processing in the field.